Yeah, getting rid of water is fairly easy. Its trying to level it out that I have trouble with. Theres an inlet near my house that looks more like white water rapids than a section of ocean. Haven't been able to figure out how to level it.

I had a similar problem when I built a pontoon dock and it was a right mess. I figured out that you have to place a dirt (or whatever) block under the top water block, then it should level out and you can remove the dirt block.

The rapids can be useful though, I use them at my docks to keep the boats from floating away.

Owain Taggart wrote:

I'm likely going to have to abandon the idea. It's just too long a tunnel to be able to fill it all with dirt, because I can only reach both ends. As soon as I get further into the tunnel, I get the air meter. If I put any dirt blocks and then take them out again, it just fills back up with water.

Nah, it should be doable, but it will take about 10 minutes. I had the same problem when I made my underwater tunnel, just do it bit by bit and the water will eventually go away. At least you don't have an 8x6x4 underwater glass station like me, that took me 20 minutes to clear of water in mine.